This invention deals with a siloxane composition used primarily for coating solid substrates. More specifically, the composition can be used to coat transparent solid substrates to render such substrates abrasion resistant and to allow such substrates to be tinted and/or dyed. The compositions of this invention when cured on solid substrates also give aesthetically pleasing, uniform, gel-free surfaces to the coated substrates.
Many solid substrates, especially clear, transparent plastic materials have been used as substitutes for glass in many applications. The reasons for this substitution are the unique properties of the plastics such as lightweightness, handleability, and ease of formation of articles.
Plastic materials are not without shortcomings, however, as most plastics are soft and scratch quite readily. In order to enable the use of plastics in some applications, it has been customary to coat the plastics with organic or silicone coatings. These coatings are, for apparent reasons, clear, unpigmented coatings. An example of such an organic coating is a heat curable polyurethane resin. The polyurethane resins are considered to be acceptable for coating plastic materials to render them abrasion resistant because eventhough the abrasion resistance of such polyurethane coatings is not as good as some siloxane-based coatings, the polyurethane coatings are less expensive.
In order to provide exceptionally hard abrasion resistant coatings to the plastic article manufacturers, new siloxane-based curable resin systems were developed. An example of such a resin system can be found in U.S. Pat. No. 3,986,997 issued Oct. 19, 1976. These siloxane resins are considered to be the premier coatings in the plastic lens and sheet market today. These coatings however have one major drawback. They do not allow tintability.
Many times, it is desirable for an end application of plastic materials if the abrasion resistant coatings can be tinted or dyed. Such uses for example include plastic sunglass lenses or bus and airplane windows.
Thus, it would be highly desirable if a method could be found to allow tintability of the premier resins, or a new resin system could be developed which would allow easy tintability of the coating and at the same time allow the coating to retain the excellent abrasion resistant properties found in siloxane-based coatings.
At least three siloxane-based resin systems have emerged in the prior art which attempt to give the desirable abrasion resistance and tintability properties. U.K. Patent Application No. 2,044,787A published Oct. 22, 1980 in the name of Ito Optical Industrial Co., Japan, discloses a coating composition containing at least one hydrolyzate of a silicon compound containing an epoxyfunctional group; a polycarboxylic acid or anhydride and a curing agent. These materials exhibit some inferior properties which will become clear when reference is made to them in the examples.
A second coating system is disclosed in U.S. Pat. No. 4,211,823 issued July 8, 1980 and assigned to Toray Industries, Inc., Tokyo, Japan. This system consists of a hydrolyzate of a silane compound which contains one epoxy group in the molecule; fine silica particles and an aluminum chelate compound. This material suffers from shelf instability, in that, the coating gels within several days after manufacture. A third coating system is a material disclosed in U.S. Pat. No. 4,073,967 issued Feb. 14, 1978 as a combination of a reactive silane and a metal ester. This material is tintable but does not offer the ultimate in abrasion resistance and handleability.